Hiding the tree when it's frozen, as done in r72665, results in its own
problems, e.g. loss of focus. So don't do this but resize the control to a
very small size when freezing it and restore it to its old size afterwards.
Closes#15166.
git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@74072 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
4e1e8dc51b